Grinding machine



March 6, 1945. s. E. WOODBURY GRINDING MACHINE Filed April 13, 1943 2Sheets-Sheet l y INVENTOR.

guy ML, m w i March 1945. s. EIWOODBURY 2,370,701

GRINDING MACHINE Filed April 15, 1943 2 Sheets-Sheet 2 162 164 v J50 196A Jr-vzr are l- 0: El 170 M 2 2' 5186i 194 i196 155% 169 his 192INVENTOR.

I J-l l What Patented Mar. 6, 1945 GRINDING moms Stephen E. Woodbury,Beverly, Mass., asslgnor to Reid Brothers Company, Inc., Beverly, Mass,a corporation of Massachusetts Application April 13, 1943, Serial No.482,838

9 Claims.

This invention relates to a grinding machine and more particularly to anelectrical control mechanism for an automatic surface grinding machine.

The invention has for an object to provide a machine tool such as agrinding machine, and particularly an automatic surface grinding machinewith a novel and improved electrical control mechanism for controllingthe operation of the machine and which is particularly useful in anautomatic surface grinding machine to enable the latter to be operatedin a safe, efficient and superior manner.

With this general object in view and such others as may hereinafterappear, the invention consists in the machine tool, and particularly thesurface grinding machine, and in the various structures, arrangementsand combinations of parts hereinafter described and particularly definedin the claims at the end of this specification.

In the drawings illustrating the preferred embodiment of the invention,Fig. l is a front elevation, partly in cross-section of a suflicientportion of a surface grinding machine embodying the present electricalcontrol mechanism to enable the invention to be understood; Fig. 2 is awiring diagram illustrating the present control mechanism as embodied ina grinding machine,

to be hereinafter more fully described; Fig. 3 is a detail view of asolenoid operated brake embodied in the present grinding machine, andFig. 4 is a modified form of braking mechanism to be referred to.

In general, a surface grinding machine embodying the invention isprovided with a longitudinal work supporting table for holding andmoving the parts to be machined with cross feed mechanism forprogressively moving the work supporting table in a transverse directionrelative to the grinding wheel. Provision is made for operating thereciprocable work supporting sition such as to overbalance the table onits support, causing damage to-the table Or the machine and possibly tothe operator. Accordingly, one feature of the present inventioncontemplates the provision of a safety or limiting switch designed to beengaged to open the electrical circuit to the driving motor when thetable approaches a dangerous position. In the preferred embodiment ofthe invention, a spring-pressed, normally closed contact member isemployed in the safety switch, so thatupon engagement thereof bylimiting stops on the table, the power is immediately cut off not onlyfrom the table motor but also from the grinding wheel motor.

In the operation of a surface grinding machine, a possibility existsthat the momentum of the table might be sumcient at times to carry thetable limiting stops beyond the safety switch whereupon the springoperated contact member would immediately reestablish the circuit andpermit continuance of the table movement. In

table through connections from a reversible motor arranged to becontrolled by the movement of the table.

In the operation of the surface grinder the table is limited in itsmovement in either direcorder to overcome this defect the safety switchis preferably placed in the circuit in series with the solenoid of theprimary magnetic switch, as will be hereinafter more fully described,whereby opening of the circuit'at the safety switch will effect openingof the primary magnetic switch, so that the safety switch will not beeffective to reestablish the connection to the driving motor in theevent that the table overrides the safety switch, as above described, oroverbalances so as to lift the limiting stops out of engagement with thesafety switch.

Another feature of the present invention relates to the provision of asolenoid operated brake in the control circuit for braking, the tabledriving motor so as to bring the latter to rest promptly uponinterruption of the circuit and thus prevent the table from coasting toa dangerous position. As above described, under normal operatingconditions, the table is limited in its movement in either direction bya reversing switch actuated by operating dogs carried by the table whichmaybe adjusted to reverse the movement of the latter at predeterminedlimits. In practice such mechanism normally operates to reverse thetable promptly at either end of its stroke. However, in prior controlmechanisms in the event that the power to the table driving motor wascut off at an intermediate point in the stroke such as by turning the"on-off switch to off or by pressing the stop button,,the table was freeto continue in motion until stopped by incidental friction. Inaccordance with the present invention, the solenoid of the solenoidoperated brake is preferably arranged in parallel with the primarymagnetic switch solenoid so that upon pressing the stop button, thetable will be brought to rest immediately at any desired position withinthe limits of its normal stroke. Furthermore, in the event that thetable should be inadvertently moved beyond its normal limits, as abovedescribed, to out off the power at the safety switch, the brake wouldlikewise be applied to prevent the table from gerous position.

Referring now to the drawings, the present invention is preferablyillustrated as embodied in a grinding machine indicated generally at Iwhich is provided with a grinding wheel I2 and a longitudinallyreciprocable work supporting table I4. The work supporting table ismounted to-slide longitudinally upon way I8 provided in-a cross slide 20which, in turn, is adapted to be moved transversely in ways 22, 24formed in the top of a casing 26 mounted upon the base 28 of themachine. The grinding wheel I2 is mounted upon a spindle I3 and isdriven by a spindle motor I as diagrammatically shown in Fig. 2.

In the illustrated surface grinding machine, the work supporting tableis arranged to be reciprocated through connections including a drivingsprocket gear 30 and a sprocket chain 82, 34 which extends around thelower part of the sprocket gear 30 and over idler sprockets 86, 38respectively and connected to lugs 40, 42 depending from the oppositeends of the table.

Provision is .made for driving and reversing coasting to a dantherotation of the sprocket gear 80 to cause the chain 32, 84 toalternately effect reciprocation of the table I4 through connectionsfrom a reversing motor 50. The gear 30 is mounted upon and arranged torotate with a driving shaft 52 which is provided with a gear 58 fastthereon arranged to mesh with a pinion 80 comprising part of a clutchmember (not shown) adapted to be operatively connected to a shaft 61.The shaft 61 is provided with a worm wheel 14 fast thereon arranged tocooperate with a worm 16 secured to the reversing motor shaft 18.

Provision is made for controlling the reversible motor 50 to efiect achange in direction thereof through connections from the reciprocablework table I4. As herein shown a reversing switch 7 I50 mounted in thecross slide is arranged to be operated by dogs I52, I54 adJustablysupported upon and movable with the table I4. The reversing switchcomprises a slidingly mounted stud I58 arranged to be reciprocated by apivotally mounted arm I58 which is received in a slot in the stud I58.An operating arm I80, fast on the pivot shaft I62 is provided with pinsI64, I65, arranged to be engaged by the dogs I52, I54 respectively atthe end of the predetermined longitudinal movement of the table. Theswitch stud I56 is provided with contacts I68, I10 and in operation,when a dog engages the switch I50, it operates to first open theprevailing circuit to the motor 50 and then close a second ,circuit tooperate the motor in the reverse direction. A handle I6I is alsoprovided on the operating arm I80 to permit the switch to be manuallyoperated when desired.

As illustrated in Figs. 1 and 2, a safety switch I12 is located beneaththe table I4 substantially centrally in the machine. It is operative toopen I14, I16 supported on the underside of thetable I4 either of whichis arranged to engage and depress the switch member I12 to-open thecircuit at contacts I18 in the event that the table should override orinadvertently fail to engage the reversing switch I50.

Referring now particularly to Fig. 2, the illus- I trated controllingapparatus comprises a primary circuit including connections to thegrinding head or spindle motor I6, and the reversing motor 50. Stop andstart switches I82, I84 are arranged to open and close a relay circuitto the solenoid I85 of a primary magnetic switch I86I81I88 which closesthe circuits to the grinding head motor and to the reversing motor atcontacts I88 and I89. The reversing switch indicated at I50 operates toalternately open one circuit and close another to the solenoids I90, I92for alternately opening and closing the circuits to the reversing motor50 at contacts I84, I95, I96 and I91 whereby the direction of rotationis reversed.

From the description thus far it will be observed that under normaloperating conditions, when the on-off" switch I98 is moved to its onposition and the start button I82 is pressed the solenoid I85 of theprimary magnetic switch I86I81-I88 is energized to close the circuits tothe spindle motor I5 and the table motor 50, and that the direction ofrotation of the motor 50 will be reversed to reciprocate the table I4each time the latter reaches its limit of movement in either directionas determined by the adjustment of the reversing dogs I52, I54. In theevent that the reversing dogs become loosened or are improperlyadjusted, or, upon failure of the reversing switch I50, the table willcontinue to be driven in the prevailing direction until either of thelimiting stops I14, I16 engages the spring-pressed safety switch I 12.As herein shown, the safety switch contacts I18 are preferably arrangedin series with the primary magnetic switch solenoid I85. With thisconstruction, when the circuit is interrupted at the safety switchcontacts I18, the primary magnetic switch solenoid will be deenergizedto open the circuits to the spindle motor I5 and the table motor. and,such circuits cannot be reestablished until two conditions aresatisfied. First, the table must be manually moved back to within itsnor-' mal range of movement to reset the safety switch contacts andsecond, the start button must be pressed. In this manner, thepossibility of reestablishing the circuit through the safety switchcontacts alone is eliminated, since, in the event the momentum of thetable should carrythe limiting stops beyond the safety switch, or, in

the event the table should be overbalanced and lift up so as to permitthe safety switch contacts to again be connected, it would still benecessary to press the start button before the circuits to the motorswould again be reestablished. In any event, positive driving of thetable beyond the limit defined by the safety switch is entirelyterminated.

- The solenoid brake, as shown in Figs. 1 and 3, and indicated generallyat 200 comprises a shoe type spring set brake which is maintained in itsinoperative or oil position when the current is on and which is releasedto apply the brake when the current is cut off. As herein shown, themotor shaft 18 may be provided with a relatively small pulley 202 andthe braking unit may be supported on a shelf 204 adjacent the motor. Inoperation, when the solenoid 206 is energized, the

brake shoes 288 are held away from the pulley to permit normal operationof the machine. However, when the circuit is interrupted as abovedescribed, the solenoid 208 is deener gized thus releasing the spring 2!to permit the brake shoes 288 to be applied to the wheel 202. Asdiagrammatically illustrated in Fig. 2, the brake solenoid 288 isarranged in parallel with the primary switch solenoid I85 so that uponinterruptionof the circuit at either the on-off switch I88, the stopbutton I84 or the safety switch I12 the brake solenoid will bedeenergized to bring the table to rest promptly.

Referring now to Figs. 1 and 4, a modified form of braking mechanism,indicated generally at 88,

comprises an electrically operated brake or friction shoe 82 adapted tofrictionally engage the underside of the work table 14 when the currentis cut off, and which is electromagnetically maintained in itsinoperative position when the current is on. As herein shown, themodified braking unit includes a. solenoid 84 arranged to hold the brakeshoe 82 down away from the underside of the table H against theresistance of a pair of coil springs 86. In the circuit shown in Fig. 2,the solenoid 84, see Fig, 4, may replace the solenoid 206 shown in Fig.2, so that in operation, when the solenoid 84 is energized, the frictionshoe 82 is held away from the reciprocable table H to permit normaloperation of the machine.

However, when the circuit is interrupted, as above described, thesolenoid 88 is deenergized thus releasing the springs 86 to apply thebrake.

From the above description it will be seen that the present inventionenables the machine to be controlled in a simple and efficient manner toprovide a maximum of safety for the operator and a minimum of liabilityof damage to the machine.

Although the present control mechanism is preferably illustrated hereinas embodied in a 2. In a grinding machine, in combination, areciprocable work supporting table, driving mechanism for reciprocatingsaid table including a reversing motor, a primary electrical circuit forsaid motor including a solenoid operated primary switch, a stopping andstarting switch for controlling the action of said primary switch, areversing switch for eifecting reversal of the motor, means carried bythe table for operating Having thus described the invention, what isclaimed is: v

1. In a grinding machina'in combination, a reciprocable work supportingtable, driving mechanism for reciprocating said table including areversing motor, a primary electrical circuit for said motor including asolenoid operated primary switch, a stopping and starting switch forcontrolling the action of said primary switch, a

reversing switch for effecting reversal of the motor, means carried bythe table for operating said reversing switch when the table is movedinto a predetermined position in either direction, and a afety switcharranged to be engaged by the table to open the circuit to the primaryswitch and thus stop the motor in the event that the table shouldinadvertently override said predetermined position, said safety switchbeing arranged in series with said primary switch solenoid whereby tointerrupt the motor circuit andprevent reestablishment thereof until thetable is moved back to within its normal range of movement and thestarting switch is operated.

.said reversing switch when the table is moved into a predeterminedposition in either direction, and a safety switch arranged to be engagedby the table to open the primary switch and thus stop the motor-in theevent that the table should inadvertently override said predeterminedposi- ,tion.

3. In a grinding machine, in combination, a reciprocable work supportingtable, driving mechanism for reciprocating said table including areversing motor, a. primary electrical circuit for said motor includinga primary magnetic switch, a stopping and starting switch controllingthe action of said primary switch, a reversing switch for efiectingreversal of the motor, a limiting dog carried at each end of said tablefor operating said reversing switch when the table is moved into apredetermined position in either direction, and a spring-pressed safetyswitch arranged to be engaged by the table to open the primary switchand thus stop the motor in the event that the table should inadvertentlyoverride said predetermined position, said safety switch being arrangedin series with the solenoid of said primary magnetic switch whereby toprevent reestablishment of said motor circuit until the ta ble is movedback to within its normal range of movement and the starting switch isalso operated.

4. In a grinding machine, in combination, a reciprocable work supportingtable, driving mechanism for reciprocating said table including areversing motor and a motor shaft, an electrical a singlecentrally'located safety switch arranged to be engaged by the table toopen the primary switch and thus stop the motor in the event that thetable should inadvertently override either of said predeterminedpositions, said safety switch being arranged in series with said primaryswitch solenoid whereby to prevent reestablishment of said motor circuituntil the table is moved back to within its normal range of movement andthe starting means is operated, a spring-actuated brake associated withsaid motor shaft, and a solenoid connected in parallel with the primaryswitch solenoid arranged to release said brake to bring said motor to anabrupt stop when said stopping means or said safety switch is operatedto interrupt the current tosaid primary switch.

5. The combination with a machine tool provided with a movable memberarranged to normally travel within predetermined limits, of drivingmechanism for said movable member including a motor, a. primary circuitfor said motor including a solenoid operated primary switch, and

switch and thus stop the motor in the event that said movable memberinadvertently overrides its normal predetermined limits.

6. The combination with a machine tool'pro-= vided with a, movablemember arranged to travel within predetermined limits, of drivingmechanism for said movable member including a motor and a motor shaft, acircuit for said motor including a solenoid operated primary switch, anda safety switch connected in series with said primary switch solenoidand arranged tobe engaged by said movable member to open said primaryswitch and thus stop the motor in the event that said movable memberinadvertently overrides its normal predetermined limits,a-spring-operated brake associated with said motor shaft, and a solenoidconnected in parallel with said primary switch solenoid arranged torelease said brake to bring said motor to an abrupt stop when saidprimary switch-is opened.

7. In a grinding machine, in combination, a reciprocable work supportingtable, driving mechanism for reciprocating said table including areversing motor, an electrical circuit for said motor including asolenoid operated primary switch, a reversing switch for effectingreversal of the motor, means carried by the table for operating saidreversing switch when the table is moved-into 4 a predetermined positionin either direction, and

a solenoid operated brake connected in parallel with the primary switchsolenoid arranged to engage said table and bring it to an abrupt stopwhen said primary switch is opened.

8. In a. grinding machine, in combination, a reciprocating work table, areversible motor for driving the table, a grinding head having anindividual motor, a primary circuit for operating both motors includingan electro-magnetic switch, means operated by the table at each end ofits normal travel, for reversing the table motor, and a single safetyswitch operated by the table in reaching a position beyond its normalpath of travel in either direction for opening said electromagneticswitch and stopping both the said motors.

9. In a grinding machine, in combination, a reciprocating table, areversible motor therefor. 23. motor circuit including primary andreversing switches, dogs carried by the'table for operating thereversing switch .at each end of the normal travel of the table, asingle safety switch located substantially centrally beneath the path oithe table for controlling said primary switch, and

separate means carried by the'table for-tripping the safety switch andoperating when the table moves in either direction beyond its normalpath 01 travel.

STEPHEN E. WQODBURY.

